The invention relates to a robot joint with an electric drive motor and a reduction gear (harmonic drive). In a known robot joint of this type the assembly flange of the flexibly deformed outer gear ring and the assembly area of the one robot part facing the same are provided with plane faces which are braced against each other with a plurality of mounting screws, whereby the torque is transmitted by the friction locking between the plane faces of the parts, as well as by the mounting screws themselves which are designed as tight-fit screws and/or by additional set pins. In these embodiments it may occur that the bores for receiving the tight-fit screws or setpins open out after a longer period of operation of the robot joint, so that an accurate positioning of the robot parts is no longer assured.